(a) Technical Field
The present invention relates to a method and system of fixing carbon dioxide. More particularly, the disclosure relates to a method for fixing carbon dioxide utilizing natural mineral or steel slag produced from ironworks, thereby reducing emission of carbon dioxide into the atmosphere.
(b) Background Art
Carbon dioxide emission is increasing rapidly due to the increased fossil fuel consumption and is recognized as the main cause of global warming. Thus, many countries in the world have been making efforts and tightening regulations to reduce carbon dioxide emissions.
The reduction in carbon dioxide emissions can be mediated by reducing the use of fossil fuel itself or by a method which separates, collects and fixes the carbon dioxide produced thereof. For the latter, utilization of the separated and collected carbon dioxide as a source for methanol synthesis, or fixing the separated and collected carbon dioxide by dumping it into the ocean or using carbonate minerals have been studied in the past.
For example, one method fixes carbon dioxide using carbonate minerals. In this method, alkaline substances (CaO, MgO, K2O, Na2O, etc.) existing in minerals are reacted with carbon dioxide to produce carbonates (CaCO3, MgCO3, Na2CO3, K2CO3, etc.) to fix the carbon dioxide emitted from plants.
Slags produced from the steelmaking process include molten iron pretreatment slag, converter slag, stainless steel slag, electric furnace slag, or the like. These steel slags are mostly buried, except for limited utilization as cement or aggregates for road or building construction. Various methods for utilizing the discarded steel slag have been proposed, as it becomes difficult to find landfills for disposal.
Korean Patent Application Publication No. 2002-0050429, entitled “Pretreatment Method Of Steel Slag By Using Carbon Dioxide,” proposes a method of fixing carbon dioxide on the surface of steel slag for use in harbor construction or artificial fish banks for fish. In another attempt to dispose of carbon dioxide using slag, Korean Patent Application Publication No. 2006-0023206 entitled, “A Method for Fixing of Carbon Dioxide,” proposes fixing carbon dioxide on the surface of slag containing a certain level of water by reacting it with carbon dioxide. However, the methods described in the above two patents require too long a reaction time since the efficiency of the reaction between carbon dioxide and slag is very low and, thus, are economically impractical.
Korean Patent No. 0891551 (Application No. 2008-0025573), entitled “Solidification Method of Carbon Dioxide By Mineral Carbonation Of Slag Generated In An Iron Industry, Capable Of Improving Reaction Efficiency,” proposes a method of solidifying carbon dioxide by carbonating alkaline components extracted from steel slag with gaseous carbon dioxide through a pressurized hydrothermal reaction or a normal-pressure hydrothermal reaction. However, the hydrothermal reaction consumes a lot of energy, and there is no clear description about how the carbon dioxide is fixed following the carbonation of the alkaline components.
Korean Patent No. 0801542 (Application No. 2006-0105753) entitled, “Method For Converting Talc For Mineral Carbonation By Removing Water Molecules And Hydroxyl Groups, And A Method For Mineral Carbonation Of Carbon Dioxide Using Talc Obtained Thereby,” proposes a method of fixing carbon dioxide using the natural mineral talc. However, since it requires a particle size of 125 μm or smaller, excessive energy is consumed for the pulverization of the mineral. Further, after the alkaline components are treated with a weakly acid solvent such as acetic acid for extraction, when pH is increased to fix the carbon dioxide through carbonation, some metal ions (e.g., Ca2+) react with hydroxide ions (OH) to form milky lime (Ca(OH)2), resulting in suspension. Thus, an additional precipitation or filtration procedure is required. Since the precipitated carbonate suspends in the solution, the separation is difficult and it is not easy to establish an industrially applicable continuous process.